Niobium alloys are useful in the space related industries because of their high strength to weight ratios at elevated temperatures. Certain alloys have been found to retain useful mechanical properties to temperatures as high as 2800.degree. F.
The benefits of achieving minimum weight in aircraft components are so significant that extreme techniques are frequently employed to achieve complex geometries and to reduce section thicknesses of components to the absolute minimum dimension permissible by design standards.
Usually, components which are fabricated from sheet or plate material of uniform thickness will have excess material in low stress regions. However, in the interest of saving weight, components are generally fabricated so that material which is not required for load support in a structure is removed.
Conventional mechanical machining techniques, such as milling, are often used to remove material, but these techniques are labor intensive, and generally require expensive machinery which must be operated by highly skilled personnel.
Nonmechanical procedures can be used for the removal of niobium in designated areas. For example, Ahn et al, in U.S. Pat. No. 4,243,476, describe a process in which an ion beam is directed toward a solid source of reactive gas species which are given off when the source is hit by the ion beam. The gases then strike the surface of the object to be etched and react with metal atoms to form volatile compounds, and remove metal from the surface of the object. This technique has been found effective for etching the surface of materials containing niobium. However, the low etch rate available when using an ion beam source and the need to perform the operation in vacuum limit the applicability of this technique.
Parissis et al, in U.S. Pat. No. 4,950,359, disclose the removal of a niobium containing coating from a copper substrate by dissolving the coating in an aqueous solution of hydrogen peroxide and an alkaline metal hydroxide. Hydrofluoric acid is commonly used in solutions selected to etch niobium alloys in order to obtain suitable etch rates. However, this solution composition was formulated without hydrofluoric acid to avoid damage to the copper substrate.